Even though anthropogenic climate change has been under way for several decades, no studies to date have directly quantified the impact of climate change on asthma morbidity - we will fill this critical knowledge gap. A recent report by the NIEHS-led Interagency Working Group on Climate Change and Health (IWGCCH) concluded that climate change will likely amplify the existing environmental triggers of asthma, resulting in more severe and frequent disease exacerbation. The working group identified several critical data gaps including the need to a) establish climate-sensitive exposure metrics, with appropriate temporal and spatial dimensions, that are most strongly associated with asthma, b) identify and map populations at increased risk of climate-related morbidity, and c) investigate the relationship between climate variables, altered plant phenology and asthma exacerbations. We will fill these critical gaps through the work of our interdisciplinary team with expertise in satelite remote sensing, climate science, public health, spatial statistics and aerobiology. Specifically, we will 1) link historical plant phenology, meteorological and air pollution data with asthma morbidity data from the National Health Interview Survey for the 1988-2010 period; 2) use the newly linked data to conduct a national scale assessment of the impact of climate change on asthma morbidity; and 3) geographically and temporally identify communities with increased risk of climate change related asthma morbidity using spatio-temporal cluster detection methodologies. The two-decades of data that we will use encompasses various natural climate modes such as El Nio-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and North Atlantic Oscillation (NAO) allowing us to investigate their impact on asthma morbidity. We will capture climate change signals using metrics likely to be strongly associated with asthma, including frequency of extreme weather events as well as changes in plant phenology that are known to respond to gradual changes in temperature and atmospheric CO2 concentration. This will enable us to - for the first time - directly quantify the impact of climate change on asthma morbidity using observed data, while adjusting for other time-varying confounders (e.g. land use change, population increases, demographic shift, access to healthcare). Using pilot funding, we have successfully linked meteorological data with NHIS respondents for 2006-2008, and begun to investigate the association between extreme weather events and asthma morbidity. Preliminary results suggest that respondents living in areas that experienced unusually hot springs days during the previous 5 years were at increased risk of hay fever (AOR=1.24 (95% CI 1.04, 1.48)) and ER visits for asthma (AOR=1.68 (CI 1.08, 2.62)). Requested funding will enable us to expand the pilot study to additional years (1988-2010) and incorporate plant phenology. The proposed study will directly address the aforementioned critical research needs identified by IWGCCH and provide for the first time, a national scale assessment of the impact of climate change on asthma morbidity based on observed data.